An ink jet recording apparatus used in a large number of printers adopts such an ink supply structure that an ink cartridge such as a cassette is put in a casing member, the ink cartridge is connected through an ink supply tube to an ink supply unit mounted on a carriage, and ink consumed in printing is supplied to a recording head through the ink supply unit including a differential pressure valve mechanism comprising a membrane valve.
By adopting this structure, according to the amount of ink consumption in the recording head, ink can be supplied to the recording head by opening and closing of the membrane valve.
However, it is very difficult to constitute the membrane valve that can correspond to the very small change of pressure produced by the ink consumption in the recording head, and does not open or close uselessly according to the vibration with a recording operation.
In order to solve such a problem, a membrane valve has been proposed as disclosed in Japanese Patent Laid-Open No. 2000-2346, which is a fluid supplying membrane valve in which a bending portion having a substantially crank-shaped section is formed in the vicinity of the periphery of a disc-shaped membrane valve having an ink supplying through-hole in its center.
According to this membrane valve, the through-hole can be brought into contact with or separated from a valve seat correspondingly to the very small differential pressure using the bending portion. However, since it is necessary for this membrane valve to simultaneously form a frame portion having a large section which functions as a support portion at its periphery, there is a disadvantage in that it is necessary to be skilled in constituting at a high accuracy the bending portion that affects elasticity of the membrane valve greatly.
Accordingly, an object of the invention is to provide an ink supply unit having a membrane valve that can be easily manufactured and can keep a valve closing state stable while it is corresponding to the very small differential pressure.
Another object of the invention is to provide the above-mentioned membrane valve.